In imaging devices, such as video camera and digital still camera, it is performed to step down the aperture of lens smaller for correct exposure (referred to as “aperture step-down” hereinafter). This aperture step-down is accompanied with two problems. First, under condition of the aperture step-down, dusts and scratches on a cover glass of a package of a pickup device and an optical low-pass filter are imaged in the form of shadows on a resultant taken image. Second, the diffractive influence of narrowed aperture on the image formation by pickup lens becomes increased.
In order to solve these problems, a light-intensity step-down device having an aperture mechanism and a ND (Neutral Density) filter is described in Patent Document No. 1. Patent Document No. 1 describes as follows, in general. The light-intensity step-down device includes a plurality of aperture blades for changing the size of an aperture opening and a ND filter disposed in an opening defined by the aperture blades and furthermore, the ND filter and the aperture blades are formed by different members, respectively. Thus, it is said that the disclosed light-intensity step-down device is capable of controlling the light intensity with high accuracy.